A conventional electric-driven air pump, such as the one disclosed in US Patent Application Publication No. 2004/0115073 A1, includes a head having a cylinder chamber, a body connected axially to the head, a motor installed within the head, a set of bevel gears driven by a shaft of the motor, and a piston assembly having linkage with the set of bevel gears. The set of bevel gears includes a small bevel gear connected to the shaft, a large bevel gear that is meshed with the small bevel gear, and a driving crank eccentrically connected to the large bevel gear. The driving crank, powered by the motor, drives reciprocal motion of the piston assembly to draw in and push air in and out of the cylinder chamber.
In order to ensure that there is enough transmission power in the air pump, the radius of the bevel gears cannot be too small. Likewise, the radius of the head and the body cannot be too small either in order to accommodate the bevel gears inside a chamber of the head. In addition, utilizing beveling gears for power transmission tends to produce grinding noise as well.